The present invention relates to a soldering flux vehicle which contains an additive to enhance fine pitch stencil printing, and to solder pastes for use in the electronics industry which are prepared using this flux vehicle and a method of fine pitch stencil printing the same.
There is a trend in the electronics industry towards the automated manufacture of printed circuit boards (PCBs) and towards the miniaturization of electronic devices with the requirement of finer and finer pitch devices. Solder paste is generally printed onto a substrate through a stainless steel or electroformed stencil. Industry standard stencils for PCB manufacture are generally about 0.125 mm or about 0.150 mm in thickness and solder pastes comprising solder powder particles of about 25 to about 45 microns in diameter are required to print about 0.25 mm diameter apertures at about a 0.5 mm pitch.
Solder paste release from a stainless steel or electroformed stencil and subsequent printed pad definition on a PCB is influenced by the chemical nature of the solder paste and, in particular, the soldering flux vehicle. A solder paste has to have a certain amount of “tack” in order that components can be placed in position on the printed solder paste pads accurately and without loss. However, the tackiness of the solder paste which holds a component in position often prevents good printing of the solder paste onto a substrate through a stencil, i.e., good aperture release of the solder paste on printing may be prevented.
Accordingly, a need continues to exist for a solder flux vehicle and solder paste formulation which have an improved release from a stencil during printing, while maintaining the internal tackiness of the solder paste thereby preventing loss of components during the assembly placement of the components onto the PCB.